Studies of the physiologic role of human placental lactogen during human pregnancy have been limited because of the potential risk of such investigations to the mother and fetus. The major goals of this proposal are 1) to investigate the effects of placental lactogen on maternal and fetal metabolism using the sheep as an in vivo animal model and 2) to investigate the humoral and/or other factors regulating the synthesis and secretion of placental lactogen in the sheep and in human placental explants cultured in vitro. To date, ovine placental lactogen has been isolated from sheep cotyledons and purified over 1000 fold. The biological properties of ovine placental lactogen appear homologous to both human placental lactogen and ovine growth hormone. Also the pattern of ovine placental lactogen secretion during pregnancy is similar to that of human placental lactogen during human pregnancy. These studies indicate that the sheep is an excellent animal model to study placental lactogen physiology.